RU Pat. No. 2051112, IPC 6 C02F1/28, issued Dec. 27, 1995, discloses a sorbent comprising a layer of zeolite treated with oxalic acid solution (0.05-0.1 mole/L) in admixture with mineral acid and brought to pH 1-2. When wastewater containing ions of heavy metals flows through a layer of the sorbent, the following level of ions removing from water is achieved: Cr (III) and Cr (VI) to 100%, Cu (II) to 98.2%, Fe (II, III) to 99.2%, Zn (II) to 98.1%.
However, the sorbent has a substantial disadvantage in that it cannot remove ions of arsenic from water, while it is found virtually in all underground and surface water sources and is extremely toxic for living organisms.
U.S. Pat. No. 6,921,732, IPC B01J 20/06, issued Jul. 26, 2005, discloses another well-known sorbent, similar to the abovementioned one in technical substance and effect, which can remove ions of arsenic (with different valence) from water. The sorbent is composed of zeolite covered with nanophase iron and manganese oxides, where 0.25-10% is iron oxide in 0.10 mole ratio of Mn/(Mn+Fe). The sorbent is produced by adding zeolite to iron-manganese solution (iron oxide solution mixed with manganiferous compound). The resultant mixture is filtered, the filtered product is dehumidified, and the final substance is the sorbent which is composed of zeolite covered with nanophase iron and manganese hydroxides.
The prototype-sorbent has the following disadvantages. It can only remove ions of arsenic, and cannot be used to remove ions of other heavy metals from water. In addition, the maximum water contamination level which allows for high degree purification is relatively low: 1.57 mg/L (ppm). Moreover, while removing ions of As(III) which is very common in nature, the sorbent releases ions of manganese Mn(II) which contaminate water.